Method of deinking

ABSTRACT

A method of deinking printed paper comprises pulping the paper to form an aqueous slurry, adding a deinking additive to the paper, and removing detached ink by flotation, wherein the additive comprises an organo-modified siloxane comprising units of the formula: [R 1   a Z b SiO (4-a-b)/2 ] n  in which each R 1  is independently selected from a hydrogen atom, an alkyl, aryl, alkenyl, aralkyl, alkaryl, alkoxy, alkanoyloxy, hydroxyl, ester or ether group; each Z is independently selected from an alkyl group substituted with an amine, amide, carboxyl, ester, or epoxy group, or a group —R 2 —(OC P H 2P ) q  (OC r H 2r ) s —R 3 ; n is an integer greater than 1; a and b are independently 0, 1, 2 or 3; R 2  is an alkylene group or a direct bond; R 3  is a group as defined for R 1  or Z above; p and r are independently an integer from 1 to 6; q and s are independently 0 or an integer such that 1≦q+s≧400; and wherein each molecule of the organo-modified siloxane contains at least one group Z.

The present invention relates to a method of deinking printedwastepaper.

Growing awareness of environmental damage caused by deforestation hasseen an increase in the recycling of wastepaper in recent years. It hasbeen recognised that the ability to recycle wastepaper is commerciallyadvantageous and has a significant impact on the conservation of virginfibre resources. However, technological advances in printing inks andprint media present ever-growing challenges to recyclers.

Printing on paper is typically accomplished using one of two types ofink, namely, impact ink, which is physically pressed onto the paper, andnon-impact ink, which is attracted to a charged image and is thentransferred to the paper. Impact inks are typically wet inks, forexample letterpress inks, offset litho inks, photogravure inks andflexographic inks. For example, letterpress inks are generally composedof carbon black pigment in a mineral oil vehicle and are used in, forexample, newspaper printing. Offset litho inks tend to contain morepigment than letterpress inks and contain drying oils such as linseed oralkyl resins. Flexographic inks are used in similar processes toletterpress inks but are water-based and contain emulsified ink in analkali soluble binder. Such inks may easily be dislodged, but may formextremely fine particles that are difficult to capture and remove.

Non-impact inks, e.g. toners, are generally dry, powdered inks and areused in laser printing, photocopying and facsimile machines andgenerally comprise thermoplastic resins and pigment.

The deinking of paper bearing these two different types of ink requiresdifferent deinking procedures and conditions. Conventionally, deinkingof paper bearing non-impact ink merely requires pulping with asurfactant in neutral conditions, whereas paper bearing impact inkrequires different conditions, such as treatment with alkali, silicateand peroxide, as well as a surfactant.

In conventional deinking methods, the wastepaper is disintegrated(pulped) by mechanical agitation in an aqueous medium to separate theink and impurities from the paper fibre and disintegrate the ink intoparticles of approximately 0.1 to 1000 μm. A grey slurry is thusobtained in which the ink is present in a finely dispersed form. Theimpurities, for example, plastic, aluminium foil, stones, screws,staples, paper clips etc., are removed during a large number ofscreening steps.

Whilst ink detachment of non-impact, e.g. photocopy, paper can normallybe achieved in neutral conditions, for other printed paper inkdetachment is routinely accomplished at alkaline pH levels using alkalihydroxides, alkali silicates, oxidative-working bleaches and surfactantsat temperatures between 30 and 50° C. Usually, anionic and nonionictensides are used as surfactants, for example, soaps, ethoxylated fattyalcohols and/or ethoxylated alkyl phenols (see, for example, EP0013758).

The ink particles are then removed from the fibre slurry by washingand/or flotation. Smaller ink particles are removed by washing, andlarger ink particles and stickies (i.e. glue residues and adhesives) areremoved by flotation. During flotation, air bubbles are blown into thepulp. The dispersed ink particles become attached to the air bubbles,which carry the ink particles to the surface. The resultant foam is thenskimmed from the surface. Subsequent steps involve heating the pulp toevenly distribute stubborn ink particles and screening the pulp toseparate the damaged, short or weak fibres. The remaining clean pulp isthen pressed between rollers into sheets and dried.

Thus, efficient deinking demands both successful separation of the inkfrom the paper fibre and removal of the dispersed ink from the fibreslurry.

However, there are a number of disadvantages associated with traditionaldeinking methods. For example, the incomplete removal of ink particlesfrom the fibre slurry can cause the resulting paper to have a grey hue,spotting, and a low degree of brightness. Brightness and colour areimportant quality criteria for many paper uses.

In addition, the alkaline conditions used in traditional deinkingmethods cause water-soluble and/or colloidal solids and finely dispersedsolids to contaminate the process water, for example, fillers, finefibres and stickies. If these contaminants are insufficiently removedduring washing, they can be concentrated by subsequent washings andreintroduced to the paper fibre, causing a loss of brightness in theresultant paper. Effluent containing the aforementioned chemicalsconventionally used in deinking methods is also environmentallyundesirable.

The present invention seeks to provide a method of deinking wastepaperwhich can overcome disadvantages of conventional deinking methods.

According to the present invention there is provided a method ofdeinking printed paper, the method comprising pulping the paper to forman aqueous slurry, adding a deinking additive to the paper, and removingdetached ink by flotation, wherein the additive comprises anorgano-modified siloxane comprising units of the formula:[R¹ _(a)Z_(b)SiO_((4-a-b)/2)]_(n)

in which each R¹ is independently selected from a hydrogen atom, analkyl, aryl, alkenyl, aralkyl, alkaryl, alkoxy, alkanoyloxy, hydroxyl,ester or ether group;

each Z is independently selected from an alkyl group substituted with anamine, amide, carboxyl, ester, or epoxy group, or a group—R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³;

n is an integer greater than 1;

a and b are independently 0, 1, 2 or 3;

R² is an alkylene group or a direct bond;

R³ is a group as defined for R¹ or Z above;

p and r are independently an integer from 1 to 6;

q and s are independently 0 or an integer such that 1≦q+s≦400;

and wherein each molecule of the organo-modified siloxane contains atleast one group Z.

Z is preferably a group —R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³,more preferably wherein p and/or r are independently 2, 3 or 4, i.e. agroup comprising ethylene, propylene, and/or butylene oxide groups.Preferably, q and s are each independently integers from 10 to 30, morepreferably 15 to 25 (for example 18). In a particularly preferred groupZ, p is 2, r is 3, and q and s are both 18. R² may be an alkylene group,for example having from 1 to 6 carbon atoms (i.e. a methylene, ethylene,propylene, butylene, pentylene or hexylene group), or a direct bond. R³may be a group as defined hereinabove for R¹ or z, and is preferably ahydrogen atom or a hydroxyl group.

Additionally or alternatively, Z may be an alkyl group substituted withan amine, amide, carboxyl, ester, or epoxy group, for example an alkylgroup having from 1 to 6 carbon atoms, i.e. a substituted methyl, ethyl,propyl, butyl, pentyl or hexyl group.

The siloxane may be linear or may comprise units in which a+b=0 or 1,i.e. the siloxane may contain branching. When Z is a group—R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³, R³ is preferably a hydroxylor alkanoyloxy group.

Preferably, 2 to 20 mole percent of silicon atoms in the siloxanemolecule are substituted by a group Z, more preferably 5 to 16 molepercent.

The siloxane preferably has a hydrophilic/lipophilic balance (HLB) inthe range of 5.0 to 7.3.

The molecular weight of the siloxane is preferably in the range of 1,000to 500,000, more preferably 10,000 to 100,000.

A particularly preferred siloxane for use in the present invention is ahydroxy-endcapped linear polydimethylsiloxane having an HLB of 5.9 to6.3, in which 10 to 12 mole percent of silicon atoms are substituted byZ groups of the formula —R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³, inwhich p is 2, r is 3 and q and s are both 18, R² is an alkylene grouphaving from 1 to 6 carbon atoms or a direct bond, and R³ is a hydrogenatom or a hydroxyl, ester or ether group.

The additive used in the present invention may comprise furthercomponents, in addition to the organo-modified siloxane. For example,the additive may further comprise one or more components selected from apolydimethylsiloxane, an organic polyether, and a fatty acid. Suitableorganic polyethers include those of the formulaR⁴—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R⁵ in which R⁴ and R⁵ areselected from a hydrogen atom, hydroxyl, alkyl and alkoxy groups, and p,q, r and s are as defined hereinabove. Suitable fatty acids includesaturated and unsaturated monobasic aliphatic carboxylic acids, forexample having from 8 to 22 carbon atoms, such as lauric, myristic,palmitic, stearic, arachidic, behenic, lignoceric, palmitolic, oleic,linoleic, linolenic, and arachidonic acids.

The additive may be in the form of an emulsion, for example theorgano-modified siloxane may be a gum based self-emulsifying siloxane.

In the method of the present invention, the additive may be added to thepaper before, during or after pulping. The amount of additive to beadded to the paper is preferably within the range 0.1 to 1 wt % of thepaper, more preferably 0.1 to 0.5 wt %. The additive may, for example,be added to the paper neat, as an emulsion, or in solution, for examplean aqueous solution.

The method of the present invention is preferably performed atsubstantially neutral pH, although the method may be performed underalkaline pH.

The pulping and ink removal steps of the present invention may beperformed as is conventional, as will be familiar to a person skilled inthe art and described hereinabove. For example, the paper may be pulpedto form an aqueous slurry having a consistency of, for example, from 1to 10% (for example, 1 to 5%) at a temperature of between 30 and 50° C.,for example 35 to 45° C. Consistency is defined as wt % of pulp solidsin the fibre suspension. Ink removal may be performed in a suitableflotation cell (for example, a Denver Lab flotation cell) at a suitabletemperature, for example between 30 and 50° C. (e.g. 35 to 45° C.), andnumber of revolutions per minute, for example from 500 to 1000 rpm. Anadditional advantage associated with the method of the present inventionis that when used to treat flexographic printed waste, the process wateris relatively clear, whereas with known deinking methods it is generallyblack. Moveover, the present method produces pulp of improvedbrightness.

Embodiments of the present invention will now be described in detail.

EXAMPLE 1

a) Pulping

To an aqueous suspension of 110 g of air-dry wastepaper (50% newspaperand 50% magazine paper) having a consistency of 4% were added 440 g ofindustrial water at 45° C. in a mixing vessel. The suspended paper waskneaded for 15 minutes at 45° C.

b) Ink Removal

Water having a hardness of 16° dH was added to the pulp obtained in a)above to achieve a consistency of 1%. To the pulp varying amounts of ahydroxyl endcapped polydimethylsiloxane having approximately 11 mole %silicon atom substitution by —(OC₂H₄)₁₈(OC₃H₆)₁₈ side chains, an HLB ofapproximately 6.1 and a molecular weight of approximately 60,000(referred to herein as Siloxane 1) was added as an aqueous solution. Thepulp was floated for 8 minutes at 45° C. in a Denver Lab Flotation Cellat 1000 rpm, after which the pulp was separated from the water, andformed into sheets between two filters of a sheet former with drying at95° C. for 10 minutes under vacuum.

By way of comparison, steps a) and b) above were repeated using acommercially available fatty acid based deinking preparation. Theresults are shown in Table 1 below. Whiteness was evaluated according toDIN 53145 Part 1. TABLE 1 wt % of Whiteness Whiteness Whiteness additivebefore after difference Additive used Paper pH flotation % flotation % %Fatty acid 0.4 aged 8.5 42.4 59.0 16.6 Fatty acid 0.4 fresh 7.2 43.651.3  7.7 Siloxane 1 0.3 aged 8.5 46.6 61.9 15.3 Siloxane 1 0.3 fresh8.5 46.6 61.9 15.3 Siloxane 1 0.3 fresh 7.2 46.5 59.1 12.6 Siloxane 10.1 fresh 7.2 44.6 56.5 11.9 Siloxane 1 0.3 aged 7.2 40.2 47.8  7.6

EXAMPLE 2

a) Pulping

To an aqueous suspension of 110 g of air-dry wastepaper (10% newspaperand 90% magazine paper) having a consistency of 20% were added 440 ml ofindustrial water at 45° C. in a mixing vessel. The suspended paper waskneaded for 15 minutes at 45° C.

b) Ink Removal

Water was added to the pulp obtained in a) above to achieve aconsistency of 1.09%. To the pulp varying amounts of a hydroxylendcapped siloxane as defined in Table 4 below were added as an aqueoussolution. The pulp was floated for 8 minutes at 45° C. in a Denver LabFlotation Cell.

Steps a) and b) above were repeated using the siloxane used in Example 1(Siloxane 1) and the siloxanes defined in Table 4 (Siloxanes 2 to 8) onfresh and aged wastepaper. Table 4 also contains viscosity data for eachof the siloxanes. By way of comparison, the experiment was also carriedout using the commercially available fatty acid based deinkingpreparation used in Example 1. The results are shown in Table 2 (freshwastepaper) and Table 3 (aged wastepaper) below. Whiteness was evaluatedaccording to DIN 53145 Part 1. TABLE 2 wt % of Whiteness WhitenessWhiteness additive before after difference Additive used pH flotation %flotation % % Fatty acid 0.4 8.1 35.8 51.1 15.3 Siloxane 1 0.3 7.5 39.456.5 17.1 Siloxane 2 0.3 7.5 39.1 54.2 15.1 Siloxane 3 0.3 7.5 40.2 55.014.8 Siloxane 4 0.3 7.5 37.8 55.0 17.2 Siloxane 5 0.3 7.5 39.0 52.6 13.6Siloxane 6 0.3 7.5 41.2 53.5 12.3 Siloxane 7 0.3 7.5 39.5 57.1 17.6Siloxane 8 0.3 7.5 40.1 54.0 13.9

TABLE 3 wt % of Whiteness Whiteness Whiteness additive before afterdifference Additive used pH flotation % flotation % % Fatty acid 0.4 7.836.3 44.6  8.3 Siloxane 1 0.3 7.3 37.0 47.8 10.8 Siloxane 4 0.3 7.3 37.050.3 13.3 Siloxane 7 0.3 7.3 37.5 48.0 10.5

TABLE 4 n (degree of % Substituted Silicon atoms polymerisation) 5 10 15100 Siloxane 2 Siloxane 3 Siloxane 4  7,720 cP  5,560 cP 3,100 cP 300Siloxane 5 Siloxane 6 Siloxane 7 98,540 cSt 6,060 cP 5,090 cP 500Siloxane 8 6,830 cP

EXAMPLE 3

a) Pulsing

To an aqueous suspension of 110 g of air-dry wastepaper (100% newspaper)having a consistency of 20% were added 400 ml of industrial water at 45°C. in a mixing vessel. The suspended paper was kneaded for 15 minutes at45° C.

b) Ink Removal

Water was added to the pulp obtained in a) above to achieve aconsistency of 1.09%. To the pulp varying amounts of a hydroxylendcapped siloxane as defined in Table 4 and Example 1 were added as anaqueous solution. The pulp was floated for 8 minutes at 45° C. in aDenver Lab Flotation Cell.

Steps a) and b) above were repeated using the siloxane used in Example 1(Siloxane 1) and two of the siloxanes defined in Table 4 (Siloxanes 4and 7). By way of comparison, the experiment was also carried out usingthe commercially available fatty acid based deinking preparation used inExample 1. The results are shown in Table 5 below. Whiteness wasevaluated according to DIN 53145 Part 1.

EXAMPLE 4

Steps a) and b) of Example 1 were repeated using the siloxane used inExample 1 (Siloxane 1), but were performed on 100% flexographic paper.In addition, 0.10 wt % sodium hydroxide and 1.20 wt % sodium silicatewere added to the slurry.

By way of comparison, the experiment was also carried out using thecommercially available fatty acid based deinking preparation used inExample 1. The results are shown in Table 6 below. The appearance of thefiltration water was also recorded. Whiteness was evaluated according toDIN 53145 Part TABLE 5 wt % of Whiteness Whiteness Whiteness additivebefore after difference Additive used pH flotation % flotation % % Fattyacid 0.4 7.7 24.7 27.0 2.3 Siloxane 1 0.3 7.3 26.5 33.0 6.5 Siloxane 40.3 7.2 24.4 33.0 8.6 Siloxane 7 0.3 7.3 26.0 35.0 9.0

TABLE 6 Whiteness Whiteness wt % of before after Whiteness Appearance ofadditive flotation flotation difference filtration Additive used % % %water Fatty acid 0.4 28.8 29.9 1.1 Dark black Siloxane 1 0.2 25.4 33.48.0 Light grey Siloxane 1 0.2 26.6 34.5 7.9 Light grey

1. A method of deinking printed paper, the method comprising pulping thepaper to form an aqueous slurry, adding a deinking additive to thepaper, and removing detached ink by flotation, wherein the additivecomprises an organo-modified siloxane comprising units of the formula:[R¹ _(a)Z_(b)SiO_((4-a-b)/2)]_(n) in which each R¹ is independentlyselected from the group consisting of a hydrogen atom, an alkyl, aryl,alkenyl, aralkyl, alkaryl, alkoxy, alkanoyloxy, hydroxyl, ester andether group; each Z is independently selected from the group consistingof (i) an alkyl group substituted with a substituent selected from thegroup consisting of an amine, amide, carboxyl, ester, or epoxy group,and (ii) a group —R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³; n is aninteger greater than 1; a and b are independently selected from thegroup consisting of 0, 1, 2 and 3; R² is selected from the groupconsisting of an alkylene group and a direct bond; R³ is selected fromthe group consisting of R¹ and Z as defined above; p and r are eachindependently an integer from 1 to 6; q and s are independently selectedfrom the group consisting of 0 and an integer such that 1≦q+s≧400; andwherein each molecule of the organo-modified siloxane contains at leastone group Z.
 2. A method according to claim 1 wherein Z is a group—R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R².
 3. A method according toclaim 2 wherein p is an integer from 2 to 4 inclusive.
 4. A methodaccording to claim 2 wherein q and s are each independently integersfrom 10 to
 30. 5. A method according to claim 4 wherein q and s are eachindependently integers from 15 to
 25. 6. A method according to claim 2wherein p is 2, r is 3, and q and s are both
 18. 7. A method accordingto claim 1 wherein R² is selected from the group consisting of amethylene, ethylene, propylene, butylene, pentylene and hexylene group.8. A method according to claim 1 wherein R³ is selected from the groupconsisting of a hydrogen atom and a hydroxyl group.
 9. A methodaccording to claim 1 wherein the siloxane is linear.
 10. A methodaccording to claim 1 wherein the siloxane contains branching.
 11. Amethod according to claim 1 wherein Z is a group—R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³, and R³ is selected from thegroup consisting of a hydroxyl and an alkanoyloxy group.
 12. A methodaccording to claim 1 wherein 2 to 20 mole percent of silicon atoms inthe siloxane molecule are substituted by a group Z.
 13. A methodaccording to claim 12 wherein 5 to 16 mole percent of silicon atoms inthe siloxane molecule are substituted by a group Z.
 14. A methodaccording to claim 1 wherein the siloxane has a hydrophilic/lipophilicbalance (HLB) in the range of about 5.0 to about 7.3.
 15. A methodaccording to claim 1 wherein the siloxane has a molecular weight in therange of about 1,000 to about 500,000.
 16. A method according to claim15 wherein the siloxane has a molecular weight in the range of about10,000 to about 100,000.
 17. A method according to claim 1 wherein thesiloxane is a hydroxy-endcapped linear polydimethylsiloxane having anHLB of about 5.9 to about 6.3, in which 10 to 12 mole percent of siliconatoms are substituted by Z groups of the formula—R²—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R³, in which p is 2, r is 3 andq and s are both 18, R² is selected from the group consisting of analkylene group having from 1 to 6 carbon atoms and a direct bond, and R³is selected from the group consisting a hydrogen atom, a hydroxyl, esterand ether group.
 18. A method according to claim 1 wherein the additivefurther comprises one or more components selected from the groupconsisting of a polydimethylsiloxane, an organic polyether, and a fattyacid.
 19. A method according to claim 18 wherein the additive furthercomprises an organic polyether of the formulaR⁴—(OC_(p)H_(2p))_(q)(OC_(r)H_(2r))_(s)—R⁵ in which R⁴ and R⁵ areselected from the group consisting of a hydrogen atom, hydroxyl, alkyland alkoxy groups, p and r are independently an integer from 1 to 6, andq and s are independently selected from the group consisting of 0 and aninteger such that 1≦q+s≧400.
 20. A method according to claim 18 whereinthe additive further comprises a fatty acid selected from the groupconsisting of a saturated and unsaturated monobasic aliphatic carboxylicacid.
 21. A method according to claim 20 wherein the carboxylic acid isselected from the group consisting of lauric, myristic, palmitic,stearic, arachidic, behenic, lignoceric, palmitolic, oleic, linoleic,linolenic, and arachidonic acids.
 22. A method according to claim 1wherein the additive is an emulsion.
 23. A method according to claim 22wherein the additive is a gum based self-emulsifying siloxane.
 24. Amethod according to claim 1 wherein the additive is added to the paperin an amount within the range 0.1 to 1 wt % of the paper.
 25. A methodaccording to claim 24 wherein the additive is added to the paper in anamount within the range 0.1 to 0.5 wt % of the paper.
 26. A methodaccording to claim 1 which is performed at substantially neutral pH. 27.A method according to claim 1 wherein the additive is added to the paperat a stage selected from the group consisting of before, during andafter pulping.
 28. A method according to claim 2 wherein r is an integerfrom 2 to 4 inclusive.
 29. A method according to claim 2 wherein both pand r are each independently an integer from 2 to 4 inclusive.